Abstract

Ionic liquids are regarded as green solvents and are often defined as molten salts with a melting point less than 100^oC. The current increased interest in ionic liquids as alternative reaction solvents is attributed to the potential engineering advantages of negligible vapour pressure and tuneable physical properties. However, for both engineers and chemists, the task of optimising reactions performed in ionic liquids is a difficult one given the vast number of these solvents potentially available as well as the problems associated with quickly obtaining the reliable kinetic data needed. Micro channel reactors (MCR) have been used successfully for high throughput chemistry, and could therefore offer a solution to this problem.

Here we will detail the kinetics obtained using a (20-40ml) well controlled Hazard Evaluation Laboratory batch reactor and compare these measurements to those obtained using MCR systems developed at the University of Sheffield. The Aza Diels Alder reaction between N-benzylideneaniline (NBA) and 2,3-dihydrofuran (DHF) to form Tetrahydroquinoline (THQ) was chosen (Figure 1(a)) as a template reaction to act as an instructive example of the scale-down effects on kinetics. This reaction was studied in in [C₂mim][NTf₂] and catalysed by Sc(OTf)₃.

(b)

(a)

           

Fig.1, (a) Aza Diels-Alder reaction studied, (b) Glass MCR

The reaction was tested using wet etched glass MCRs (Figure 1(b)) fitted with the required services and controls. The results to be presented from large-scale batch studies and the small scale MCR tests showed water played a very important role in both the reaction mechanism and the physical behaviour of the solvents. In the case of the MCR system control and the use of refined and well executed procedures proved to be critical.